1. Field of Invention
This invention relates to fire protection systems and specifically to a novel inflatable bag apparatus for deploying gaseous and vaporizable fire extinguishing and explosion suppression agents.
2. Prior Art
Several basic mechanisms for effecting fire extinguishing and explosion suppression for various combustible fuel/oxidizer combinations exist. These are: (a) separation of fuel from the oxidizer (typically air) e.g. mechanical fire fighting foam agents; (b) dilution of oxidizer to a concentration below which it cannot support combustion e.g. with an inert gas such as helium; (c) cooling of the reactants (fuel and oxidizer) and sufficient absorption of the thermal energy output to quench the combustion process e.g. by application of water spray; and (d) the chemical inhibition of the production of free radicals essential to the sustenance of the combustion process e.g. by a chemical agent such as bromotrifluoromethane (CF3Br). Agent selection, storage, quantity and dispensing method are affected by the particular fire protection problem or application which, in turn, dictates operational (environment; habitable vs. non- habitable, etc.) and system weight, volume and cost constraints, e.g. ground facilities versus aircraft applications.
In general, fire extinguishing agents are applied in either (a) a local application mode such as from a portable hand held fire extinguisher or from a turret on a fire fighting vehicle, or (b) a total flooding mode such as by the rapid distribution of a fire extinguishing agent via fixed nozzles into a confined space so as to achieve a concentration level in air throughout the entire volume sufficient for fire extinguishment.
Modern aircraft turbine engine installations are representative of a confined space fire protection application and are considered natural "fire zones" because of the inherent presence of an ignition source(s) and the close proximity of flammable/combustible fluids such as jet fuel, engine oil and, in many instances, hydraulic fluid. The "fire zone" designation requires that overheat/fire detection and in the case of most multiengine aircraft, fire extinguishing systems be provided for protection of crew, passengers and equipment. These protection systems are in addition to the rigorous application of fire prevention and hardening measures such as unidirectional, high velocity air flow to purge volatile combustible fluid leaks while also reducing the likelihood of hot surface ignition, and suitable fire walls to prevent fire penetration into adjacent compartments. Fire detection systems respond in the matter of a few seconds. Fire extinguishing systems once activated also respond very rapidly and are designed to discharge a halon chemical fire extinguishing agent such as bromotrifluoromethane (CF.sub.3 Br) into the compartment so as to achieve a certain minimum volume percent concentration (6% for CF.sub.3 Br; varies with the particular agent used) simultaneously at all locations in the engine compartment and hold that concentration for a short time (approximately 0.5 second) to achieve extinguishment. The fire extinguishing system typically entails a bottle to store the fire extinguishing agent under pressure, an open ended distribution conduit leading to an appropriate location within the "fire zone" and an electro-mechanical valve or electro-explosive (squib) rupture diaphragm incorporated into the neck of the bottle for triggering release of the agent. No provision is incorporated to terminate engine compartment ventilation air in the event of fire; consequently, determination of agent quantity requirements for a particular installation entails consideration of several factors but, in particular, engine compartment free volume and ventilating air flow (as a function of flight profile). Overall agent effectiveness is reduced (quantity increased) by agent leakage out and/or air leakage into the fire control area thereby decreasing agent dwell time and by agent/air mixing inefficiencies. No apparatus is known, however, which simultaneously overcomes these agent/air mixing inefficiencies.
Military and civil aircraft currently employ halon agents such as bromotrifluoromethane (Halon 1301) and bromochlorodifluoromethane (Halon 1211) in on-board fire extinguishing systems for the protection of engine installations and other areas designated as "fire zones". These agents evolved from industry and principally Department of Defense (DOD) research and development efforts which were begun in the 1950's and provide outstanding fire extinguishing effectiveness and other favorable toxicologic, operational and system attributes which made them essentially the "universal" choice for these applications. Unfortunately, these same extinguishants, upon release into the atmosphere, have been tabbed in recent years to possess characteristics which make them extremely bad actors from the standpoint of depleting the "critical" ozone level in the earth's stratosphere and consequently has led to an international ban on their future production. Effective (cost and performance) alternative fire protection techniques are urgently needed for aircraft flight safety and survivability to fill the void resulting from the banning of these halon "chemical" extinguishants.
There are several on-going efforts which are directed at the identification and evaluation of alternative and replacement materials for the Halon 1301 and 1211 agents for both aircraft and ground fire protection applications. Candidates under consideration include perfluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, hydrobromofluorocarbons, iodofluorocarbons, dry chemicals, carbon dioxide, nitrogen and mixtures of basically inert gases. It is generally accepted that the development of "true" replacements for halons 1301 and 1211 for aircraft and ground applications is not imminent.